Incorrect right click processing in MSA Editor

Scenario to reproduce:

1. Open "data/samples/CLUSTAWL/COI.aln".
2. Select any base.
3. Move the mouse to another base and click the right button.
   Expected state: a context menu appears, a single base from the previous step is selected.
4. Move the mouse to the any third base and click the left button.
   Expected state: the context menu closes, the first selected base is the only selected base.
   Current state: the context menu closes, there is a selection from the base from the second step to the base from the last step.